1. Field of the Invention
The present invention relates to a novel valve gate injection molding apparatus having a hot runner assembly.
2. Brief Description of the Prior Art
In general, a valve-gate injection molding apparatus has a valve pin adapted to open and close a gate which injects a resin melt into a mold cavity. The base end of the valve pin is allowed to be open or closed by a reciprocally movable actuating means such as a hydraulic cylinder or a piston mounted within a fixed side mounting plate. Approximately half a length of the valve pin is within a hot runner which serves as a resin melt passage and surrounded by the heated and pressurized resin melt.
In addition, by mounting a manifold on the mounting plate, and providing a plurality of heated nozzles on the manifold, it is possible to perform a multiple molding operation to achieve high productivity with increased number of gates, that is, with a number of mold cavities.
However, in the conventional molding apparatus mentioned above, the gas produced from the melt .and the heated and pressurized melt itself are likely to leak through the gap between the receiving hole of the heated nozzle and the inner surface of the valve pin in the direction from the outer surface to the base of the valve pin.
The produced gas, which will degrade the quality of molded products, should be discharged out of the heating probe. The leak of the resin melt, which will disturb the molding function of the valve pin or other members, also should be prevented. Also, the valve pin actuating means should be prevented from various troubles caused by overheat due to heat conduction from the heated and pressurized resin melt.
To prevent the advantages stated above, for example, the Japanese patent publication No. 59-47653(1984) relating to "A push seal for a valve pin" discloses a valve pin, for which a stepped portion is provided for preventing the resin melt from Flowing into the sliding portion between the heating probe and valve pin, and the seal is provided by the shoulder formed as a result of the stepped portion. A disadvantage still remains therein, that the resin melt tends to flow into the sliding portion during operation of the valve pin.
Japanese laid-open patent publication No. 63-107528(1988) relating to "Valve gate multiple injection molding apparatus" discloses an assembly for staying the leaking resin in a dish-shaped bushing to prevent it from its outboard leaking. However, the method therein is not suitable for a long time operation.
Japanese patent publication No. 4-6532(1992) also relating to "Valve gate multiple injection molding apparatus" discloses a cooling means for the hydraulic cylinder of the valve pin actuating assembly. This structure enables cooling adjacent the cylinder, but still disables thermal isolation of the heating manifold.